The correct answer is D. Elder.


1. Context of the Sentence:
- The sentence is talking about the brother in relation to the speaker, specifically regarding his age compared to the speaker.

2. Word Meanings:
- Elder: Refers to someone older than another person, used in a familial or personal context to compare age among siblings.
- Older: Generally refers to being greater in age but is not typically used in this context.
- Oldest: Refers to the person who is the most advanced in age among a group but is used for comparisons among more than two people.
- Senior: Refers to someone holding a higher rank or status, not age.

3. Usage in the Sentence:
- "Elder" is the most appropriate term for comparing the age of siblings, as in "My elder brother intends to get married in June."

So, the sentence correctly becomes: "My elder brother intends to get married in June."